The invention relates to radiation-curable inner and outer primary optical glass fiber coating compositions. The invention also relates to coated optical glass fibers and optical glass fiber assemblies. More particularly, the invention relates to a ribbon assembly having improved ribbon stripping capabilities.
Optical glass fibers are usually coated with two superposed radiation-cured coatings, which together form a primary coating. The coating which contacts the glass surface is called the inner primary coating and the overlaying coating is called the outer primary coating.
The inner primary coating is usually a soft coating having a low glass transition temperature (hereinafter xe2x80x9cTgxe2x80x9d), to provide resistance to microbending. Microbending can lead to attenuation of the signal transmission capability of the coated optical glass fiber and is therefore undesirable. The outer primary coating is typically a harder coating providing desired resistance to handling forces, such as those encountered when the coated fiber is cabled.
For the purpose of multi-channel transmission, optical glass fiber assemblies containing a plurality of coated optical fibers have been used. Examples of optical glass fiber assemblies include ribbon assemblies and cables. A typical optical glass fiber assembly is made of a plurality of coated optical glass fibers which are bonded together in a matrix material. For example, the matrix material can encase the optical glass fibers, or the matrix material can edge-bond the optical glass fibers together.
Optical glass fiber assemblies provide a modular design which simplifies the construction, installation and maintenance of optical glass fibers by eliminating the need to handle individual optical glass fibers.
Coated optical glass fibers for use in optical glass fiber assemblies are usually coated with an outer colored layer, called an ink coating, or alternatively a colorant is added to the outer primary coating to facilitate identification of the individual coated optical glass fibers. Such ink coatings and colored outer primary coatings are well known in the art. Thus, the matrix material which binds the coated optical glass fibers together contacts the outer ink layer if present, or the colored outer primary coating.
When a single optical glass fiber of the assembly is to be fusion connected with another optical glass fiber, or with a connector, an end part of the matrix layer can be removed to separate each of the optical glass fibers.
Desirably, the primary coatings on the coated optical glass fibers, and the ink coating if present, are removed simultaneously with the matrix material to provide bare portions on the surface of the optical glass fibers (hereinafter referred to as xe2x80x9cribbon strippingxe2x80x9d). In ribbon stripping, the matrix material, primary coatings, and ink coating, are desirably removed as a cohesive unit to provide a clean, bare optical glass fiber which is substantially free of residue. This residue can interfere with the optical glass fiber ribbon mass fusion splicing operation, and therefore usually must be removed by wiping prior to splicing. However, the step of removing the residue can cause abrasion sites on the bare optical glass fiber, thus compromising the strength of the connection. The superior stripping functionality of ribbon assemblies to provide clean, residue-free, bare optical glass fibers during ribbon stripping according to this invention has heretofore been believed to be unobtainable.
A common method for practicing ribbon stripping at a terminus of the ribbon assembly is to use a heated stripping tool. Such a tool consists of two plates provided with heating means for heating the plates to about 90 to about 120 C. An end section of the ribbon assembly is pinched between the two heated plates and the heat of the tool softens the matrix material and the primary coatings on the individual optical glass fiber. The heat-softened matrix material and heat-softened primary coatings present on the individual optical glass fibers can then be removed to provide bare optical glass fiber ends, at which the fusion connections can be made. A knife cut is often used to initiate a break in the matrix material to the inner primary coating. Typically, only about a 1 to 4 cm section of the matrix material and coatings on the optical glass fibers need be removed. Identification of the bare individual optical glass fibers achieved by tracing back along the bare optical fiber until the ink coating or colored outer primary coating is seen.
U.S. Pat. No. 5,373,578 discloses a ribbon assembly containing a plurality of coated optical glass fibers. Each of the optical glass fibers is coated with an inner primary coating which is adjacent to the optical glass fiber, with an outer primary coating and an ink coating on the outer primary coating. The inner primary coating is modified so that adhesion between the inner primary coating and the optical glass fiber is reduced. This reduction in adhesion facilitates easy removal of the heat-softened primary coating when using a heat stripping method. While this patent discloses, at column 5, lines 10-13, that the adhesion between the inner primary coating and the optical glass fiber should be sufficient to prevent delamination of the inner primary coating from the optical glass fiber, any reduction in the adhesion between the inner primary coating and the optical glass fiber increases the possibility of such undesirable delamination, especially in the presence of moisture. Delamination of the inner primary coating from the optical glass fiber can lead to degraded strength of the optical glass fiber as well as signal transmission attenuation disadvantages.
Published European patent application 0262340 discloses a ribbon cable having a xe2x80x9cpeel layerxe2x80x9d as the outermost coating layer on each of optical glass fibers contained within the ribbon cable. During ribbon stripping, the peel layer is destroyed and the matrix material is removed from the coated optical glass fibers. However, after ribbon stripping, the optical glass fibers are still coated with the primary coatings. That is, the primary coatings are not simultaneously removed with the matrix material in the ribbon assemblies disclosed in this publication.
U.S. Pat. No. 5,011,260 discloses a ribbon cable having a xe2x80x9cdecoupling layerxe2x80x9d disposed between the coated optical glass fibers and the matrix material. In this manner, the matrix material may be easily removed from the coated optical glass fibers by application of low stripping force. This patent includes a general statement that the coatings on the optical glass fiber can be simultaneously removed with the matrix material during ribbon stripping. However, this patent fails to teach how to solve the problems associated with the residues remaining on the bare optical glass fibers after ribbon stripping conventional ribbon assemblies.
Published European patent application 0407004 discloses a ribbon cable containing a matrix material having sufficient adhesion to the ink coated optical glass fibers to remain adhered thereto during normal use but is easily strippable therefrom without damaging the integrity of the ink layer on the coated optical glass fibers. Thus, the ribbon assembly disclosed in this publication does not have the capability of removing the primary coatings on the optical glass fibers simultaneously with removal of the matrix material during ribbon stripping, so as to provide residue-free bare optical glass fibers.
Published European patent application 0527266 discloses a ribbon cable containing a lubricating xe2x80x9cinterfacial layerxe2x80x9d which separates the matrix material from the coated optical glass fibers. The interfacial layer facilitates easy removal of the matrix material from the coated optical glass fibers. While this publication discloses at page 3, line 15, that the buffer layer and first protective coating can be stripped in one step, there is no disclosure teaching how to accomplish such an operation. Furthermore, the lubricating interfacial layer will inhibit simultaneous removal of the first protective coating with the matrix material. Thus, this publication does not teach how to make a ribbon assembly having the capability of removing the primary coatings on the optical glass fibers simultaneously with the matrix material during ribbon stripping, so as to provide residue-free bare optical glass fibers.
U.S. Pat. No. 4,900,126 discloses a ribbon cable in which the bonding adhesive forces between the ink layer and the primary coatings on the optical glass fibers are greater than the bonding between the ink layer and the matrix material. In this manner, the matrix material can be easily removed from the ink coated optical glass fibers without removing the ink layer. However, this patent does not address the problems associated with removing the primary coating layers simultaneously with the matrix material.
U.S. Pat. No. 4,660,927 teaches a silicone-coated optical fiber in which the soft silicone coating is easily peeled from the surface of the optical glass fibers by finger pressure. The coating contains a first siloxane component having aliphatic unsaturated groups and a second siloxane component having mercaptoalkyl groups. Because such a coating is easily peelable, as by rubbing with finger pressure, the coating has insufficient adhesion to the surface of the optical glass fibers to prevent delamination during most uses. Furthermore, this patent does not address the problems of ribbon stripping, but rather only the stripping of a single optical glass fiber. It is generally known that three coating systems (inner primary coating, outer primary coating, and ink coating) having acceptable single fiber strippability will exhibit dramatically different levels of strippability characteristics when used in ribbon form.
U.S. Pat. No. 4,496,210 provides a radiation-curable optical fiber coating composition containing a polysiloxane. However, this patent does not address the problems associated with ribbon stripping.
Japanese Patent Application H3-35210 teaches to combine a liquid lubricant, such as liquid silicone oil or liquid aliphatic oil, with a mercaptosilane compound in an inner primary coating composition. During stripping, when the bond between the surface of the optical glass fiber and inner primary coating is broken the liquid lubricant invades the boundary between the surface of the optical glass fiber and the inner primary coating. The liquid lubricant must not have a high compatibility with the inner primary coating or it will not bleed out of the inner primary coating during stripping. However, this document fails to teach a system to adjust the level of fiber friction between the adjacent surfaces of the optical glass fiber and the inner primary coating to a level which provides a resistive force that is less than the cohesive strength of the inner primary coating. Thus, while this document teaches that the inner primary coating can be stripped more easily by incorporating liquid lubricant compounds, the inner primary coating will still leave unwanted residue on the surface of the optical glass fiber if the above described fiber friction forces are at a level which provide a resistive force that is greater than the cohesive strength of the inner primary coating.
One primary coating composition available from JSR Corporation, designated as R-1055, is specified as having, inter alia, a viscosity of 5000 cps @ 25xc2x0 C., a glass transition temperature of xe2x88x924xc2x0 C., a shrinkage value of 2.9%, a tensile strength value of 0.21 kg/mm2, a tensile elongation value of 195%, an adhesion force of 20 g/cm and a Young""s modulus @ 23xc2x0 C. of 0.12 kg/mm2. When this composition was tested in accordance with the test methods herein, it had a measured crack propagation value of 1.56 mm (standard deviation 0.2), and a fiber pull-out friction value of 26.3 g/mm (standard deviation 1.65).
There are many test methods which may be used to determine the performance of a ribbon assembly during ribbon stripping. An example of a suitable test method for determining the stripping performance of a ribbon is disclosed in the article by Mills, G., xe2x80x9cTesting of 4- and 8-fiber ribbon strippabilityxe2x80x9d, 472 International Wire and Cable Symposium Proceedings (1992), the complete disclosure of which is incorporated herein by reference.
Many attempts have been made to understand the problems associated with ribbon stripping and to find a solution to increase ribbon stripping performance. The following publications attempt to explain and solve the problems associated with ribbon stripping: K. W. Jackson, et. al., xe2x80x9cThe Effect of Fiber Ribbon Component Materials on Mechanical and Environmental Performancexe2x80x9d, 28 International Wire and Symposium Proceedings (1993); H. C. Chandon, et. al., xe2x80x9cFiber Protective Design for Evolving Telecommunication Applicationsxe2x80x9d, International Wire and Symposium Proceedings (1992); J. R. Toler, et. al., xe2x80x9cFactors Affecting Mechanical Stripping of Polymer Coatings From Optical Fibersxe2x80x9d, International Wire and Cable Symposium Proceedings (1989); and W. Griffioen, xe2x80x9cStrippability of Optical Fibersxe2x80x9d, EFOC and N, Eleventh Annual Conference, Hague (1993).
The ability of a ribbon assembly to ribbon strip cleanly so as to provide bare optical glass fibers that are substantially free of residue is still unpredictable and the factors affecting ribbon stripping are not fully understood. There is still a need for an understanding of how the problems of ribbon stripping occur and a solution to these problems.
It is an objective of the present invention to provide a novel ribbon assembly having improved ribbon stripping capabilities. It is another objective of the present invention to provide a novel ribbon assembly which after ribbon stripping provides bare optical glass fibers which are substantially free of residue, that must be removed prior to forming connections to the respective selected bare optical fibers.
Surprisingly, the above objects and other objects are and have been obtained by the following. The present invention provides a novel ribbon assembly comprising:
a plurality of coated optical glass fibers, at least one optical glass fiber coated with at least an inner primary coating and an outer primary coating, and optionally an ink coating; and
a matrix material bonding said plurality of coated optical glass fibers together, wherein said inner primary coating is adapted to provide the combination of properties of:
(i) sufficient adhesion to said optical glass fiber to prevent delamination during handling and in the presence of moisture; and
(ii) a fiber friction force between said optical glass fiber and said inner primary coating which has been so adjusted as to allow the inner primary coating to slide readily off from the optical glass fiber while leaving substantially no residue on the surface of said optical glass fiber during ribbon stripping, when a stripping force which is less than the cohesive strength of said inner primary coating is applied to said ribbon assembly.
Also provided is a novel ribbon assembly comprising:
a plurality of optical glass fibers, at least one coated optical glass fiber coated with at least an inner primary coating and an outer primary coating, and optionally an ink coating; and
a matrix material bonding said coated optical glass fibers together,
and wherein said inner primary coating is adapted to provide a fiber pull-out friction of about 30 grams/millimeter or less at a rate of about 0.1 mm/sec in combination with a crack propagation characteristic of at least about 1 millimeter at a rate of 0.1 mm/sec.
The present invention further provides a coated optical glass fiber comprising:
an optical glass fiber;
an inner primary coating on the surface of said optical glass fiber;
an outer primary coating substantially co-extensive with the external surface of said inner primary coating, wherein said inner and outer primary coatings are so formulated and selected so as to provide a ratio of (i) the change in length of the inner primary coating from an ambient temperature to a ribbon stripping temperature to (ii) the change in length of the outer primary coating from said ambient temperature to said ribbon stripping temperature of less than about 1.5:1; and
optionally an ink coating adjacent to said outer primary coating.
The invention further relates to a ribbon assembly containing at least one of these coated optical glass fibers.
The present invention further relates to a novel radiation-curable oligomer which can be used to adjust the fiber friction to a level such that the resulting adhesive resistive force level is less than the cohesive strength of the inner primary coating. The novel radiation-curable oligomer comprises:
at least one glass coupling moiety;
at least one slip agent moiety; and at least one radiation-curable moiety, wherein said glass coupling, glass adhesion, and radiation curable moieties are each covalently linked to said oligomer.
Also provided is a radiation-curable, inner primary coating composition containing the composite oligomer, a coated optical glass fiber made from the coating composition, and a ribbon assembly containing at least one such coated optical glass fiber.
The present invention also provides a radiation-curable, inner primary coating composition comprising at least one radiation-curable oligomer or monomer and a wax. Preferably, the wax is present in an amount sufficient to provide a fiber friction between an inner primary coating formed from said coating and an optical glass fiber such that there is exhibited a resistive force that is less than the cohesive strength of said coating formed from said composition. The invention also provides a coated optical glass fiber having an inner primary coating which contains a wax, and a ribbon assembly which contains at least one such coated optical glass fiber.
The present invention further provides a coated optical glass fiber having an inner primary coating which has been formulated from a radiation-curable, inner primary coating composition containing a radiation-curable silicone oligomer or a silicone compound. Preferably, the radiation-curable silicone oligomer or silicone compound is present in an amount sufficient to provide a fiber friction between the inner primary coating and the optical glass fiber such that there is exhibited a resistive force which is less than the cohesive strength of the inner primary coating. The invention also provides a ribbon assembly which contains at least one such coated optical glass fiber.
The present invention also provides a coated optical glass fiber having an inner primary coating which has been formulated from a radiation-curable, inner primary coating composition containing a radiation-curable fluorinated oligomer or a fluorinated compound. Preferably, the radiation-curable fluorinated oligomer or fluorinated compound is present in an amount sufficient to provide a fiber friction between the inner primary coating and the optical glass fiber such that there is exhibited a resistive force that is less than the cohesive strength of the inner primary coating. The invention further provides a ribbon assembly which contains at least one such coated optical glass fiber.
The present invention also provides a radiation-curable, inner primary coating composition comprising at least one radiation-curable oligomer or monomer and a solid lubricant which is substantially insoluble in the composition. Preferably, the solid lubricant is present in an amount sufficient to provide a fiber friction between an inner primary coating formed from said coating and an optical glass fiber such that there is exhibited a resistive force which is less than the cohesive strength of said coating formed from said composition. The invention also provides a coated optical glass fiber having an inner primary coating which contains a solid lubricant, and a ribbon assembly which contains at least one such coated optical glass fiber.
The present invention further provides a ribbon assembly comprising a plurality of coated optical glass fibers, at least one optical glass fiber coated with at least an inner primary coating and an outer primary coating, and optionally an ink coating, and a matrix material bonding said plurality of coated optical glass fibers together. The inner primary coating is formulated from a radiation-curable inner primary coating composition containing at least one radiation-curable urethane oligomer comprising at least one polymeric block and at least one functional group capable of polymerization in the presence of actinic radiation connected to said at least one polymeric block. The coating composition has a concentration of urethane groups which is selected to provide said inner primary coating with a fiber friction force level between said optical glass fiber and said inner primary coating in combination with a crack propagation level that provides the inner primary coating with the functional capability of sliding off of the optical glass fiber and leaving substantially no residue on the surface of said optical glass fiber during ribbon stripping when a stripping force which is less than the cohesive strength of said inner primary coating is applied to said ribbon assembly.
The present invention further provides a ribbon assembly comprising a plurality of coated optical glass fibers, at least one optical glass fiber coated with at least an inner primary coating and an outer primary coating, and optionally an ink coating, and a matrix material bonding said plurality of coated optical glass fibers together. The inner primary coating is formulated from a radiation-curable inner primary coating composition containing at least one radiation-curable oligomer comprising at least one polymeric block and at least one functional group capable of polymerization in the presence of actinic radiation connected to said at least one polymeric block. The polymeric block has a molecular weight which is selected to provide said inner primary coating with a fiber friction force level between said optical glass fiber and said inner primary coating in combination with a crack propagation level that provides the inner primary coating with the functional capability of sliding off of the optical glass fiber and leaving substantially no residue on the surface of said optical glass fiber during ribbon stripping when a stripping force which is less than the cohesive strength of said inner primary coating is applied to said ribbon assembly.
The invention also provides a radiation-curable, inner primary coating composition formulated from a composition comprising at least one urethane oligomer having at least one polymeric block and at least one functional group capable of polymerization in the presence of actinic radiation connected to said at least one polymeric block. The coating composition has a concentration of urethane groups that is so selected to provide said inner primary coating with a fiber friction force level between an optical glass fiber and an inner primary coating formed from said coating composition in combination with a crack propagation level which provides the inner primary coating with the functional capability of sliding off the optical glass fiber and leaving substantially no residue on the surface of said optical glass fiber during ribbon stripping when a stripping force which is less than the cohesive strength of said inner primary coating is applied to said inner primary coating.
The present invention further provides a radiation-curable, inner primary optical glass fiber coating composition formulated from a composition comprising at least one radiation-curable oligomer having at least one polymeric block and at least one functional group capable of polymerization in the presence of actinic radiation connected to said at least one polymeric block. The polymeric block has a molecular weight so selected to provide said inner primary coating with a fiber friction force level between said optical glass fiber and said inner primary coating in combination with a crack propagation level that provides the inner primary coating with the functional capability of sliding off the optical glass fiber and leaving substantially no residue on the surface of said optical glass fiber during ribbon stripping when a stripping force which is less than the cohesive strength of said inner primary coating is applied to said inner primary coating.
The present invention also provides coated optical glass fibers containing at least one inner primary coating formed from the above radiation-curable, inner primary coating compositions.